A conventional ultrasonic probe comprises a plurality of transducers that transmit ultrasonic waves and receive reflected echoes thereof, a backing member provided on the back surfaces of the transducers so that ultrasonic waves transmitted from the transducers will not return back again, an acoustic matching layer formed on the front surfaces of the transducers to match the difference between the acoustic impedance of the transducers and the acoustic impedance of the living body, and an acoustic lens provided on the upper surface of the acoustic matching layer to converge the ultrasonic beam. The plurality of transducers are formed in the shape of short strips which are linearly arranged in a one-dimensional manner, or in a two-dimensional manner, or are so arranged in many number that the ultrasonic wave transmitting/receiving surfaces are formed in an arcuate shape, thereby to constitute an ultrasonic probe.
The scanning of the ultrasonic beam by the above-mentioned ultrasonic probe is effected in combination of an ultrasonic transmission beam and an ultrasonic reception beam by driving the ultrasonic probe. That is, transmission signals that are time delayed are added to the transducers, to form an ultrasonic transmission beam that converges the ultrasonic waves at a given point, and the reflected echo signals received by the transducers are delayed to effect the phasing thereby to form an ultrasonic reception beam. Furthermore, an ultrasonic beam in the direction of short axis of the transducers arranged in many number is converged through an acoustic lens or the like to control the slicing thickness of the tomographic image. Moreover, two to four ultrasonic reception beams are used in combination for an ultrasonic transmission beam of one direction, to increase the number of scanning lines of the ultrasonic beams, thereby attempting to shorten the scanning time and to improve the resolution of the ultrasonic image. In order to obtain a three-dimensional image, furthermore, the two-dimensional scanning of the ultrasonic beam is effected a plural number of times in the slicing direction with respect to the subject.
By using the conventional ultrasonic probe, however, the ultrasonic transmission beam exhibits directivity. Besides, with the transducers of the conventional shape and arrangement, ultrasonic waves called grating lobes are generated in the transverse direction in addition to main lobes. Therefore, the directivity of the ultrasonic transmission beam is often deteriorated. The presence of the grating lobes causes a difference in the sensitivity among the ultrasonic beams when the number of the ultrasonic beams is increased by using a plurality of ultrasonic reception beams. Due to the difference in the sensitivity, therefore, limitation is imposed on the number of the ultrasonic reception beams and, hence, limitation is imposed on accomplishing a high frame rate of the obtained ultrasonic image. In obtaining a three-dimensional diagnostic image by using the conventional ultrasonic probe, furthermore, it is not often allowed to three-dimensionally diagnose the moving portion of the subject due to limitation on the number of the ultrasonic beams and limitation on increasing the frame rate.
In order to cope with the above-mentioned problems, therefore, the object of the present invention is to provide an ultrasonic probe which enables the improvement of directivity of an ultrasonic transmission beam by reducing the grating lobes at the time of transmitting ultrasonic waves, and an ultrasonic diagnostic apparatus using the ultrasonic probe as a probe for transmitting and receiving ultrasonic waves to and from a diagnosing part of a subject.